During tunnel lining construction, it is very difficult to position the reinforcing steel bars of the side wall while reinforcement binding, and it is impossible to accurately perform a three-dimensional positioning for the reinforcing steel bar. Problems often occur that the spacing between two reinforcing steel bars is not constant, the thickness of the protective layer of the reinforcing steel bar is too large or too small, the reinforcing steel bars press against the waterproof board to cause puncture of the waterproof board, and the excessive cutting stock causes waste of the reinforcing steel bars etc., which seriously affects the quality of the lining construction, resulting in poor durability of the tunnel structure. There are some reinforcing steel bar positioners in the prior art, but these reinforcing steel bar positioners cannot absolutely position the reinforcing steel bars (i.e., three-dimensional positioning in the X, Y and Z directions), the spacing between two reinforcing steel bar positioners is difficult or impossible to adjust, and the inner reinforcing steel bars and the outer reinforcing steel bars of the side wall cannot be simultaneously positioned (especially in the case that the reinforcing steel bars of the side wall have different heights). A method and device for three-dimensional accurate positioning of the reinforcing steel bar of the side wall has not been found.